Network nodes forward data. Network nodes may take the form of one or more routers, one or more bridges, one or more switches, one or more servers, or any other suitable communications processing device. The data is commonly formatted as messages and forwarded using forwarding tables. A message is a formatted unit of data that typically contains control information and payload data. Control information may include information that identifies sources and destinations, such as addresses, error detection codes like checksums, sequencing information, etc. Control information is typically found in message headers and trailers. Payload data is typically located between the message headers and trailers. Depending on factors such as the network level and network protocol used, a message may be formatted and/or referred to as one of various specific types such as packets, datagrams, segments, or frames.
Operation of routing mechanisms within a network can be described in terms of a “control plane” and a “data plane.” The data plane, also referred to as the “forwarding plane,” does the actual forwarding of messages coming into a node. Data plane decisions may involve accessing a forwarding table that relates the appropriate message identifier to the specific network interface, or egress interface, the message should be sent to in order to send it in the right direction. Generating such a forwarding table, based on a map, database, or other information reflecting the topology of the network, is a function of the control plane.
The control plane generates and updates its network topology information using one or more routing protocols. Within an autonomous system, an interior gateway protocol (IGP) can be used for exchanging network topology information between nodes. An autonomous system, or routing domain, as used herein refers to a collection of interconnected network nodes under a common administration for purposes of network configuration. Exchange of routing information between autonomous systems can be done using an exterior gateway protocol such as Border Gateway Protocol (BGP).
The processes involved in forwarding messages in networks may vary depending on the forwarding configuration used. Overall forwarding configurations include unicast, broadcast, and multicast forwarding. Unicast is a method of point-to-point communication most often used when a particular node (known as a source) has instructions to send data to another particular node (known as a receiver) and is not concerned with sending the data to multiple receivers. Broadcast is method used when a source has instructions to send data to all receivers in a domain, and multicast allows a source to send data to a group of receivers in a domain while preventing the data from being sent to other receivers in the domain.
Multicast is the preferred method of data forwarding for many popular applications, such as streaming media distribution. One reason for this is that multicast is a bandwidth-conserving technology that allows delivery of data to multiple receivers while avoiding transmission of multiple copies of the same message over the same network link. However, in traditional multicast systems, a relatively large amount of control plane information is used. Setting up and maintaining this control information has a tendency to become complex and costly in terms of computing resources, and can become a major limiting factor in overall network performance.